1. Field of Invention
The present invention relates to a semi-active suspension system of a vehicle, and more particularly, to a method for measuring a vertical acceleration of a semi-active suspension system.
2. Description of the Prior Art
In general, a semi-active suspension system is an apparatus for improving the driving stability and ride comfort of a vehicle by changing the dynamic characteristics of dampers mounted in a vehicle in real time. When a driver excessively steers a vehicle or the movement of the vehicle is out of its path, load unbalance of the vehicle causes the vehicle to be biased or not to be steerable so that the driver may be in unpredictable danger such as vehicle overturn. However, when a vehicle, which is mounted with the semi-active suspension system, drives on an uneven road, a vertical load at a contact surface of a tire and the road is kept at an appropriate level, so that the stability of the vehicle can be secured in steering, braking and driving. In addition, irregular shocks generated from the road when the vehicle travels are effectively absorbed, so that the ride comfort and driving convenience can be provided to a passenger and a driver.
Such a semi-active suspension system controls actuators and dampers respectively connected to four road wheels after detecting the driving conditions of the vehicle through vertical acceleration sensors, vehicle velocity sensors, a steering angle sensor, a brake sensor, a throttle position sensor, and the like among a variety of sensors mounted to the vehicle.
Among them, the vertical acceleration sensors are installed adjacent to four dampers. However, since there is a difference between the practical mounting positions of the acceleration sensors and the installation positions of the dampers, it is difficult to accurately measure the accelerations of the road wheels.
In a prior art, three vertical accelerations are measured through two vertical acceleration sensors mounted in front of a vehicle body and a vertical acceleration sensor mounted at the rear thereof in the vicinity of the respective dampers, and a fourth vertical acceleration is obtained in such a manner that an ECU receives the three vertical accelerations and calculates the other vertical acceleration using Equation 1 as follows:
                                          a            RL                    =                                    a              RR                        +                                                            t                  R                                                  t                  F                                            ·                              (                                                      a                    FL                                    -                                      a                    FR                                                  )                                                    ,                            (        1        )            where aFL is a vertical acceleration of a front left side, aFR is a vertical acceleration of a front right side, aRL is a vertical acceleration of a rear left side, aRR is a vertical acceleration of a rear right side, tF is a front tread, and tR is a rear tread.
Since it is difficult to accurately obtain a fourth vertical acceleration through calculation using the three vertical accelerations and the threads of the road wheels, there is a problem with accurate determination of the dynamic characteristics of the vehicle.
Further, in the prior art, there is also a problem in that it is difficult to accurately obtain a velocity even upon calculation thereof from three velocity sensors.